Tetrahydrofuran (hereinafter, sometimes simply referred to as “THF”) is used as a solvent for various organic compounds and is known to be a compound useful also as a raw material of a polyether polyol such as polytetramethylene ether glycol.
As the industrial production method of a cyclic ether such as tetrahydrofuran, a variety of production methods have been conventionally known, but among others, the cyclic ether is produced in many cases by dehydration cyclization of a dihydroxy compound such as 1,4-butanediol (hereinafter, sometimes simply referred to as “1,4BG”). As the catalyst for the dehydration cyclization reaction of a dihydroxy compound, an acid catalyst is known to be effective in view of high conversion ratio and selectivity, and, for example, Patent Document 1 describes a method where an alkanediol such as 1,4-butanediol is dehydrogenated and dehydrated in the presence of a cobalt-containing catalyst, an organic sulfonic acid and a high-boiling-point amine to produce an α,β-cyclic unsaturated ether such as dihydrofuran. Also, Patent Document 2 describes a method for continuously producing THF by a reaction of a 2-(4-hydroxybutoxy)tetrahydrofuran-containing 1,4BG reaction mixture on a heteropolyacid catalyst.
The raw material 1,4-butanediol used for THF production can be obtained by conventionally known various production methods of 1,4BG, and with respect to the product 1,4BG obtained, a byproduct occurring in the production process may be slightly mixed as an impurity into the product 1,4BG. The kind or amount of the impurity varies depending on the production method of 1,4BG, and Patent Document 2 discloses that when 1,4BG containing 2-(4-hydroxybutoxy)tetrahydrofuran which is one of impurities is used as a raw material to produce THF, a high-boiling-point component occurs as a byproduct in the reactor for THF production. Also, Patent Document 3 discloses that a water-containing crude product obtained by hydrogenating 1,4-butynediol contains gamma butyrolactone other than 1,4BG, and it is stated that the gamma butyrolactone is separated from the crude product by using a distillation column.